/* 齿轮 · 交互式图解 —— 原创样式 */
:root {
  --bg: #0b0c0f;
  --bg-soft: #101216;
  --panel: #14161b;
  --line: #23262d;
  --ink: #e8e9ed;
  --ink-dim: #a2a7b3;
  --ink-faint: #6b7079;
  --accent: #ff6b5e;
  --accent-2: #ffb04d;
  --teal: #46d6c6;
  --blue: #67a8ff;
  --violet: #b48cff;
  --radius: 12px;
  --col: 42rem;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  font-size: 18px;
  line-height: 1.9;
  letter-spacing: .01em;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* ---------- 阅读进度 ---------- */
.progress {
  position: fixed; inset: 0 0 auto 0; height: 2px; z-index: 50;
  background: transparent; pointer-events: none;
}
.progress i {
  display: block; height: 100%; width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width .1s linear;
}

/* ---------- 页头 ---------- */
.hero {
  max-width: var(--col); margin: 0 auto; padding: 14vh 1.5rem 3rem;
}
.hero .eyebrow {
  font-size: .78rem; letter-spacing: .22em; text-transform: uppercase;
  color: var(--accent); margin: 0 0 1.4rem;
}
.hero h1 {
  font-size: clamp(3rem, 9vw, 5.5rem);
  line-height: 1.02; letter-spacing: -.03em;
  margin: 0 0 1.2rem; font-weight: 700;
}
.hero .sub {
  font-size: clamp(1.05rem, 2.4vw, 1.35rem);
  line-height: 1.7; color: var(--ink-dim); margin: 0 0 2rem; max-width: 30em;
}
.hero .meta {
  font-size: .85rem; color: var(--ink-faint);
  border-top: 1px solid var(--line); padding-top: 1.2rem; margin: 0;
}

/* ---------- 目录 ---------- */
.toc {
  max-width: var(--col); margin: 0 auto 2.5rem; padding: 0 1.5rem;
}
.toc ol {
  list-style: none; margin: 0; padding: 0;
  display: grid; grid-template-columns: repeat(auto-fill, minmax(15rem, 1fr));
  gap: .1rem 2rem; border-top: 1px solid var(--line); padding-top: 1.4rem;
}
.toc a {
  display: flex; gap: .8rem; align-items: baseline;
  color: var(--ink-dim); text-decoration: none;
  padding: .42rem 0; font-size: .93rem; border-bottom: 1px solid transparent;
  transition: color .15s;
}
.toc a:hover { color: var(--ink); }
.toc a b {
  font-variant-numeric: tabular-nums; font-weight: 500;
  color: var(--ink-faint); font-size: .78rem; min-width: 1.4em;
}

/* ---------- 正文 ---------- */
main { padding: 0 1.5rem 4rem; }

section.chapter {
  max-width: var(--col); margin: 0 auto;
  padding: 3.2rem 0 1rem;
}
section.chapter > .num {
  font-size: .78rem; letter-spacing: .2em; color: var(--ink-faint);
  margin-bottom: .6rem; font-variant-numeric: tabular-nums;
}
h2 {
  font-size: clamp(1.6rem, 4vw, 2.1rem);
  line-height: 1.25; letter-spacing: -.02em;
  margin: 0 0 1.3rem; font-weight: 650;
}
h3 {
  font-size: 1.16rem; line-height: 1.5; letter-spacing: -.01em;
  margin: 2.6rem 0 .9rem; font-weight: 600;
}
p { margin: 0 0 1.35rem; }
a { color: var(--accent-2); text-decoration: none; border-bottom: 1px solid rgba(255,176,77,.3); }
a:hover { border-bottom-color: var(--accent-2); }
strong { font-weight: 650; color: #fff; }
em { font-style: normal; color: var(--accent-2); }
code, .mono {
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: .88em; background: #1a1d23; padding: .12em .4em;
  border-radius: 4px; color: #d8dbe2;
}
.eq {
  display: block; text-align: center; margin: 1.8rem 0;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: 1rem; color: #dfe2e8; letter-spacing: .02em;
  padding: 1.1rem; background: var(--bg-soft); border-radius: 8px;
  border: 1px solid var(--line); overflow-x: auto;
}
.note {
  border-left: 2px solid var(--accent); padding: .2rem 0 .2rem 1.1rem;
  color: var(--ink-dim); font-size: .95rem; margin: 1.8rem 0;
}
.note b { color: var(--ink); }

/* ---------- 演示面板 ---------- */
.demo {
  margin: 2.6rem 0 2.8rem;
  width: min(64rem, calc(100vw - 3rem));
  margin-left: 50%;
  transform: translateX(-50%);
}
.demo-inner {
  background: linear-gradient(180deg, #12141a 0%, #0e1014 100%);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: .9rem .9rem .2rem;
  box-shadow: 0 20px 60px -30px rgba(0,0,0,.9);
}
.demo-canvas {
  position: relative; width: 100%; aspect-ratio: 16 / 9;
  border-radius: 8px; overflow: hidden;
  background: radial-gradient(120% 120% at 50% 0%, #15181e 0%, #0b0c0f 70%);
  touch-action: pan-y;
}
.demo-canvas canvas {
  display: block; width: 100%; height: 100%;
  cursor: grab;
}
.demo-canvas canvas.dragging { cursor: grabbing; }

.demo-controls {
  display: flex; flex-wrap: wrap; gap: .5rem 1.6rem;
  padding: .85rem .3rem .7rem; align-items: center;
}
.demo-controls:empty { display: none; }

/* 控件 */
.ctl {
  display: grid; grid-template-columns: auto; gap: .15rem;
  min-width: 9.5rem; flex: 1 1 9.5rem; max-width: 16rem;
}
.ctl-head {
  display: flex; justify-content: space-between; align-items: baseline;
  font-size: .74rem; letter-spacing: .08em; color: var(--ink-faint);
}
.ctl-head .val {
  color: var(--teal); font-variant-numeric: tabular-nums;
  font-family: ui-monospace, Menlo, monospace; font-size: .8rem;
  letter-spacing: 0;
}
input[type=range] {
  -webkit-appearance: none; appearance: none;
  width: 100%; height: 18px; background: transparent; margin: 0; cursor: ew-resize;
}
input[type=range]::-webkit-slider-runnable-track {
  height: 2px; background: #2c3038; border-radius: 2px;
}
input[type=range]::-webkit-slider-thumb {
  -webkit-appearance: none; width: 13px; height: 13px; margin-top: -5.5px;
  border-radius: 50%; background: #eceef2;
  box-shadow: 0 0 0 4px rgba(255,255,255,.06), 0 1px 6px rgba(0,0,0,.6);
  transition: box-shadow .15s, transform .1s;
}
input[type=range]:hover::-webkit-slider-thumb {
  box-shadow: 0 0 0 6px rgba(255,107,94,.18), 0 1px 6px rgba(0,0,0,.6);
}
input[type=range]:active::-webkit-slider-thumb { transform: scale(1.15); }
input[type=range]::-moz-range-track { height: 2px; background: #2c3038; }
input[type=range]::-moz-range-thumb {
  width: 13px; height: 13px; border: none; border-radius: 50%; background: #eceef2;
}

.btn {
  font: inherit; font-size: .8rem; letter-spacing: .04em;
  color: var(--ink-dim); background: #1a1d23;
  border: 1px solid var(--line); border-radius: 999px;
  padding: .38rem .95rem; cursor: pointer;
  transition: color .15s, border-color .15s, background .15s;
  white-space: nowrap;
}
.btn:hover { color: var(--ink); border-color: #3a3f49; }
.btn[aria-pressed=true] {
  color: var(--accent-2); background: rgba(255,176,77,.1);
  border-color: rgba(255,176,77,.5); font-weight: 600;
}
.btn-row { display: flex; gap: .45rem; flex-wrap: wrap; }

figcaption, .demo figcaption {
  font-size: .85rem; line-height: 1.75; color: var(--ink-faint);
  padding: .7rem .35rem .4rem; max-width: 58rem;
}
.demo figcaption b { color: var(--ink-dim); font-weight: 500; }

/* 数据表 */
.data {
  width: 100%; border-collapse: collapse; font-size: .88rem;
  margin: 1.2rem 0 2rem;
}
.data th, .data td {
  text-align: left; padding: .55rem .6rem; border-bottom: 1px solid var(--line);
  font-variant-numeric: tabular-nums;
}
.data th { color: var(--ink-faint); font-weight: 500; font-size: .78rem; letter-spacing: .08em; }
.data td:first-child { color: var(--ink-dim); }

/* ---------- 页脚 ---------- */
footer {
  max-width: var(--col); margin: 0 auto; padding: 3rem 1.5rem 6rem;
  border-top: 1px solid var(--line); color: var(--ink-faint); font-size: .87rem;
}
footer p { margin: 0 0 .7rem; }
footer .sig { color: var(--ink-dim); }

/* ---------- 响应式 ---------- */
@media (max-width: 720px) {
  body { font-size: 17px; line-height: 1.85; }
  .demo { width: 100vw; margin-left: 50%; }
  .demo-inner { border-radius: 0; border-left: 0; border-right: 0; padding: .5rem .5rem .1rem; }
  .demo-canvas { aspect-ratio: 4 / 3; }
  .ctl { max-width: none; }
  section.chapter { padding-top: 2.4rem; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}

/* 目录当前章节 */
.toc a.active {
  color: var(--ink);
  border-bottom-color: var(--accent);
}
.toc a.active b { color: var(--accent); }

/* 全局暂停按钮 */
.pause-all {
  position: fixed; right: 1.1rem; bottom: 1.1rem; z-index: 60;
  font: inherit; font-size: .8rem; letter-spacing: .02em;
  color: var(--ink-dim); background: rgba(18,20,25,.92);
  border: 1px solid var(--line); border-radius: 999px;
  padding: .5rem 1rem; cursor: pointer;
  -webkit-backdrop-filter: blur(10px); backdrop-filter: blur(10px);
  box-shadow: 0 8px 30px -12px rgba(0,0,0,.9);
  transition: color .15s, border-color .15s, background .15s;
}
.pause-all:hover { color: var(--ink); border-color: #3a3f49; }
.pause-all[aria-pressed=true] {
  color: var(--accent-2); border-color: rgba(255,176,77,.5);
  background: rgba(255,176,77,.08);
}
@media (max-width: 720px) {
  .pause-all { right: .8rem; bottom: .8rem; font-size: .75rem; padding: .45rem .8rem; }
}

/* ---------- 入场动画（仅在有 JS 时启用，避免无脚本时空白） ---------- */
.js .demo-inner {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity .75s cubic-bezier(.2, .7, .2, 1),
              transform .75s cubic-bezier(.2, .7, .2, 1);
  will-change: opacity, transform;
}
.js .demo-inner.in { opacity: 1; transform: none; }
.js .demo figcaption { opacity: 0; transition: opacity .9s ease .15s; }
.js .demo figcaption.in { opacity: 1; }
@media (prefers-reduced-motion: reduce) {
  .js .demo-inner, .js .demo figcaption { opacity: 1; transform: none; transition: none; }
}

/* ---------- 滚动叙事 ---------- */
.scrolly {
  /* 从 42rem 的正文栏里挣脱出来，占满视口 */
  width: min(76rem, calc(100vw - 3rem));
  margin-left: calc(50% - min(38rem, (100vw - 3rem) / 2));
  margin-top: 3.5rem;
  margin-bottom: 5rem;
  display: grid;
  grid-template-columns: minmax(16rem, 24rem) minmax(0, 1fr);
  gap: 3.5rem;
  align-items: start;
}
.scrolly-media { position: sticky; top: 8vh; grid-column: 2; grid-row: 1; }
.scrolly-steps { grid-column: 1; grid-row: 1; }
.scrolly-media .demo {
  width: 100%; margin: 0; transform: none;
}
.scrolly-media .demo-inner { padding: .7rem .7rem .1rem; }
.scrolly-steps { padding: 4vh 0 24vh; }
.step {
  min-height: 54vh;
  display: flex; flex-direction: column; justify-content: center;
  opacity: .28;
  transition: opacity .55s ease;
}
.step.active { opacity: 1; }
.step h3 {
  font-size: .95rem; margin: 0 0 .7rem; letter-spacing: .06em;
  color: var(--accent-2); font-weight: 600;
}
.step p {
  font-size: .96rem; line-height: 1.85; margin: 0; color: var(--ink-dim);
  transition: color .55s ease;
}
.step.active p { color: var(--ink); }

@media (max-width: 900px) {
  .scrolly { display: block; width: 100%; margin: 1.5rem 0 3rem; margin-left: 0; }
  .scrolly-media {
    position: sticky; top: 0; z-index: 6;
    background: linear-gradient(180deg, var(--bg) 70%, rgba(11,12,15,.92) 100%);
    padding: .35rem .5rem .55rem;
  }
  .scrolly-media .demo-canvas { aspect-ratio: 16 / 10; }
  .scrolly-steps { padding: 1vh 1.25rem 14vh; }
  .step { min-height: 44vh; opacity: .3; }
  .step.active { opacity: 1; }
}

/* ---------- 键盘可见焦点 ---------- */
.btn:focus-visible,
.pause-all:focus-visible,
input[type=range]:focus-visible {
  outline: 2px solid var(--accent-2);
  outline-offset: 3px;
}